Distribution shifts in Indo-Pacific humpback dolphins and the co-occurrence of marine heatwaves

Abstract

Global ocean warming and extreme climate events pose a severe threat to marine biodiversity by inducing species redistribution and ecosystem reorganization. It is important to quantify the impacts of marine heatwaves (MHWs) on marine cetacean habitats to avoid rapid ecosystem shifts. Here we utilized detected breakpoints and early warning indicators derived from sightings data spanning from 2009 to 2021 to assess the distribution change of Indo-Pacific humpback dolphin (Sousa chinensis). We found that (1) during the 2014 MHWs, the encounter rates (number of on-effort sightings per 100 km) of humpback dolphins in Hong Kong waters significantly decreased, with the breakpoint occurring during the autumn of 2014; (2) Since 2014, Hong Kong waters have experienced more prolonged and frequent MHWs, with a significant reduction of core habitat by 26%; according to Granger causality analysis, changes in sea surface temperature drove shifts in dolphin distribution; (3) Our analysis revealed a co-existence of rapid annual increases in MHWs and high habitat usage, with the marine park located in Southwest Lantau being particularly at risk. This study on dolphin distribution shifts and their relationships with marine heatwaves in Southern China made a contribution to our understanding of the action of marine cetaceans' response to climate change. Additionally, it highlights the importance of considering MHWs in dolphin conservation efforts.